The present invention relates to a drum cleaning apparatus for an electrostatic copying machine.
In an electrostatic copying machine of the type utilizing a dry development process, a photoconductive drum is electrostatically charged and a light image is radiated onto the surface of the drum to form an electrostatic image through localized photoconduction. A dry toner substance comprising ferromagnetic carrier particles and non-magnetic toner particles is applied to the drum to form a toner image thereon. The toner image is transferred to a copy sheet and fixed thereto to provide a permanent reproduction of the original document. Thereafter, the drum is discharged and residual toner substance removed therefrom.
One of the most effective means for removing the residual toner substance is a magnetic brush. Such a magnetic brush comprises a non-magnetic cylinder which is rotated in close proximity to the drum. Magnets are provided inside the cylinder. Due to the force of the magnets carrier particles, in which the lower portion of the cylinder is immersed, adhere to the cylinder to form a magnetic brush. The magnetic brush brushingly engages with the cylinder to remove the residual toner particles therefrom. Advantages of such a magnetic brush drum cleaning apparatus include high cleaning efficiency and no damage to the drum since the brushing engagement is very light.
However, a problem has heretofore remained unsolved in such a magnetic brush cleaning apparatus in that with prolonged use the proportion of toner particles in the magnetic brush substantially increases. In other words, the toner particles accumulate in the magnetic brush. This causes fatigue of the carrier particles and a deterioration in the cleaning efficiency. In order to prevent double printing which would result from insufficient cleaning of the drum, it has heretofore been necessary to frequently replace the carrier particles in the cleaning apparatus. This constitutes inefficient use of the carrier particles and an excessive maintenance requirement.